Various spherical annular seal members used in spherical pipe joints for automobile exhaust pipes have been disclosed in, for example, JP-A-54-76759, JP-A-6-123362, JP-A-10-9396, JP-A-10-9397, and the like.
As compared with a bellows-type joint, each of the proposed spherical annular seal members is capable of reducing the manufacturing cost and excels in durability. However, each of these spherical annular seal members is formed such that a heat-resistant material formed of expanded graphite and the like and a reinforcing member made from a metal wire net are compressed to fill meshes of the metal wire net of the reinforcing member with the heat-resistant material such that the heat-resistant material and the reinforcing member are integrally formed in mixed form. Therefore, in addition to the problem of leakage of exhaust gases through the spherical annular seal member itself due to such as the proportion of the reinforcing member to the heat-resistant material and the degree of compression of the heat-resistant material and the reinforcing member, there is an inherent problem in that abnormal noise can occur due to the presence of the heat-resistant material at the partially convex spherical surface which slidably abuts against a mating member. For example, if the proportion of the reinforcing member to the heat-resistant material is excessively large, or the degree of pressurization of the heat-resistant material is low, the degree of sealing by the heat-resistant material with respect to infinitesimal passages occurring around the reinforcing member declines, resulting in initial leakage. Moreover, there is a possibility of early leakage of exhaust gases due to such as the oxidation and wear of the heat-resistant material at high temperatures. In addition, if the heat-resistant material at the partially convex spherical surface has been pressurized to a high degree, or the proportion of exposure of the heat-resistant material with respect to the reinforcing member at the partially convex spherical surface is extremely large, stick-slip can result, possibly causing the occurrence of abnormal noise.
The present invention has been devised in view of the above-described aspects, and its object is to provide a spherical annular seal member which makes it possible to eliminate the leakage of exhaust gases through the spherical annular seal member itself, and which makes it possible to eliminate the occurrence of abnormal noise and has a stable sealing characteristic, as well as a method of manufacturing the same.